1. Field of the Invention
In at least one aspect, the present invention relates to a method of using a liquid catalyst system to prepare a supported catalyst with the liquid catalyst dispersed onto a solid carrier.
2. Background Art
The chemical industry uses a wide variety of transition metal complexes as catalysts for organic reactions. Olefin polymerization is an important example of such a reaction. A number of different catalyst systems are used in the polymer and plastics industries. Such catalysts systems include, for example, single-site (metallocene and non-metallocene) catalysts and Ziegler-Natta catalysts. Historically, polyolefins have been made with Ziegler catalyst systems that include transition metal-containing compounds and one or more organometallic compounds. For example, titanium trichloride and diethylaluminum chloride have been used to form polyethylene. Similarly, a catalyst system containing titanium tetrachloride, vanadium oxytrichloride, and triethylaluminum is also effective for making polyethylene. The single site catalysts are generally more desirable since they are more reactive and produce polymers with improved physical properties. Single site catalysts tend to form polymers with a narrower molecular weight distribution, a lower concentration of low molecular weight components, more uniform comonomer incorporation and lower density. Moreover, Ziegler-Natta catalysts tend to produce polymers having a broad molecular weight distribution which may be undesirable for such molding operations as injection molding.
Metallocene catalysts include one or more π-bonded ligands such as cyclopentadienyl groups or boraaryl groups. This type of ligand has been found to have significant effects on the active catalyst site. Late transition metal (groups 8–10) single-site catalysts are also known. Numerous other catalysts for various other polymerizations are also known. Such catalysts include, for example chromium based catalysts, vanadium based catalysts such as vanadium oxychloride and vanadium acetylacetonate, cationic forms of metal halides, such as aluminum trihalides and cobalt based catalysts.
Some polymerization processes such as gas phase and slurry polymerization generally require a support to control polymer particle size and to prevent fouling of the reactor walls. Suitable supports include, for example, inorganic oxides, inorganic chlorides, and polymeric resins such as polystyrene, styrene-divinylbenzene copolymers, and the like. Such carriers contain some polar groups to assist in attachment to the catalysts. The most widely used supports are inorganic oxides of the Group 2, 3, 4, 5, 13, or 14 elements. Catalysts are attached to these supports by a number of techniques. For example, the organometallic component of a catalyst may be dissolved in a solvent and contacted with the support. Subsequently, the solvent is removed by evaporation. In an alternative method, an activator is deposited on the support either separate from or together with an organometallic compound.
Treated or untreated supports can be used. However, it is preferred to pretreat the support by thermal (calcined) or chemical methods. For example, calcination is typically performed at a temperature greater than about 150° C. Chemical agents which may be used to pretreat a support include organoaluminums, organosilanes, organoboranes, organomagnesiums, organozinc compounds and the like. Preferred chemical agents include alumoxanes, hexamethyldisilazane, trimethylchlorosilane, Grignard reagents, and triethylboron. Although these methods of applying a support work reasonably well, there is a tendency even after support pre-treatment for clumping of the catalysts to occur. Such clumping interferes with the efficiency of the catalysts and accordingly is undesirable.
Accordingly, there exists a need for an improved method of contacting and dispersing a liquid catalyst onto a solid support or carrier.